Methods for producing crucibles with a reduced amount of bubbles

ABSTRACT

Methods for producing crucibles for holding molten material that contain a reduced amount of gas pockets are disclosed. The methods may involve use of molten silica that may be outgassed prior to or during formation of the crucible. Crucibles produced from such methods and ingots and wafers that are produced from crucibles with a reduced amount of gas pockets are also disclosed.

FIELD OF THE DISCLOSURE

The field of the disclosure relates to methods for producing cruciblesfor holding molten material that contain a reduced amount of gaspockets, to crucibles produced from such methods and to ingots andwafers that are produced from such crucibles. In some embodiments, themethods involve use of molten silica that may be outgassed prior to orduring formation of the crucible.

BACKGROUND

Single crystal wafers (e.g., silicon single crystal wafers) are used asa substrate upon which electronic devices (e.g., integrated circuits)are built. Single crystal wafers may be produced by slicing the wafersfrom a single crystal ingot and subjecting the sliced wafers to variousfinishing operations such as various lapping, grinding, etching, andpolishing steps to produce the finished wafers. Such ingots may be grownby the Czochralski method in which polycrystalline silicon is firstmelted within a quartz crucible. After the polycrystalline silicon hasmelted and the temperature equilibrated, a seed crystal is dipped intothe melt and subsequently extracted to form a single crystal siliconingot while the quartz crucible is rotated.

Device manufacturers increasingly require wafers that do not contain gaspockets at the surface of the wafer upon which devices are built. Suchgas pockets in the wafer result from gas bubbles in the silicon meltbeing incorporated into the growing ingot during pulling of the siliconingot. One source of such bubbles is gas pockets (i.e., bubbles) withinthe quartz crucible. Molten silicon slowly etches the quartz cruciblewhich allows the gas therein to exit the crucible and enter the siliconmelt. Some gases (e.g., oxygen) can dissolve into the melt beforeincorporation into the ingot. However, some less soluble gases (e.g.,argon which is typically used as an insulating gas in the crystal pullchamber) dissolve at a slower rate and the gas bubble becomesincorporated into the silicon ingot thereby forming a gas pocket in theingot.

A continuing need exits for silicon ingots and wafers with reduced gaspockets as well as crucibles that result in less gas bubbles beingincorporated into the silicon ingot during ingot growth. A continuingneed also exists for methods for producing crucibles that allow ingotsand wafers with less gas bubbles to be produced.

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the disclosure, which aredescribed and/or claimed below. This discussion is believed to behelpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentdisclosure. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

SUMMARY

One aspect of the present disclosure is directed to a process forproducing a crucible for holding molten material. The crucible has abase and one or more sidewalls. A source of silica is melted to producea molten composition comprising silica. The molten composition is moldedinto the shape of (1) a crucible having a base and one or moresidewalls, (2) a plate or (3) a tube. The molten composition is cooledto solidify the composition. When the molten composition is molded intothe shape of a plate or a tube, the plate or tube is shaped into theform of a crucible having a base and one or more sidewalls.

Various refinements exist of the features noted in relation to theabove-mentioned aspects of the present disclosure. Further features mayalso be incorporated in the above-mentioned aspects of the presentdisclosure as well. These refinements and additional features may existindividually or in any combination. For instance, various featuresdiscussed below in relation to any of the illustrated embodiments of thepresent disclosure may be incorporated into any of the above-describedaspects of the present disclosure, alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a crucible with a surface layer.

DETAILED DESCRIPTION

In various embodiments of the present disclosure, a crucible that issubstantially free of bubbles may be formed by melting a source ofsilica and by outgassing gases from the molten silica prior to or duringmolding of the silica composition into a silica crucible. In otherembodiments, a crucible is formed by contacting a crucible substrate(e.g., fused silica) with a gas that contains gaseous silicon and oxygenand depositing silica onto the surface of the crucible to form a surfacelayer on the crucible that is substantially free of bubbles.

It should be noted that, as used herein, “molten” silica and/or a silica“melt” refer to silica that has been heated to a point at which thesilica can be molded to take the shape of an object (i.e., may bereferred to as being “plastic”) such as by use of force (e.g., by use ofa paddle) and these terms are not intended to require a particulardegree of silica flowability. Additionally, the term “melting” isintended to refer to a process in which silica is heated to atemperature at which silica may be molded to take the shape of an objectand is not intended to imply that the material be present in a fully“liquid” state. Further, it should be noted that the terms “silica” and“quartz” as used herein are synonymous and refer to material composed ofsilica, i.e., SiO₂, and the term “quartz” should not be limited toquartz mineral. Further, the phrases “gas pockets” and “gas bubbles”which may be used in reference to the morphology of the crucible or ofsilicon ingots or wafers produced when using a crucible of the presentdisclosure refer to any detectable void in the material and are intendedto be synonymous.

To prepare crucibles, a source of silica is melted to produce a moltencomposition. Generally any source of silica available to those of skillin the art may be used such as quartz sand, quartz powder, reclaimedglass or cullet. The source of silica may include at least about 10 wt %silica therein and, in other embodiments, contains at least about 25 wt%, at least about 50 wt %, at least about 75 wt %, at least about 85 wt%, at least about 95 wt %, at least about 99 wt %, from about 10 wt % toabout 100 wt %, from about 50 wt % to about 100 wt %, from about 85 wt %to about 100 wt % or from about 95 wt % to about 100 wt % silica. Insome embodiments, the source of silica consists essentially of silica(i.e., the source contains only silica and minor amounts of impurities).The source of silica may include fining agents (e.g., arsenic oxides,antimony oxides, KNO₃, NaNO₃, NaCl, fluorides or sulfates) to preventbubble formation. Such fining agents may be present in the source ofsilica in an amount less than about 3 wt % or less than about 1 wt %.

The source of silica may contain relatively low amounts of impuritiesthat can become incorporated into the silicon melt and the growingsilicon ingot. High purity silica can be obtained commercially, forexample, high purity ingots or tubing that is produced under the brandGE Type 214 (Momentive (Columbus, Ohio)). Such tubing may be melted ormolded directly into the form of a crucible as described further below.Typical amount of impurities in GE Type 214 quartz is shown in Table 1below.

TABLE 1 Purity amounts for commercial sources of high purity silica.Element Amount (ppm) Al 14 As <0.002 B <0.2 Ca 0.4 Cd <0.01 Cr <0.05 Cu<0.05 Fe 0.2 K 0.6 Li 0.6 Mg 0.1 Mn <0.05 Na 0.7 Ni <0.1 P <0.2 Sb<0.003 Ti 1.1 Zr 0.8 —OH (hydroxyl) <5

It should be noted that the purity amounts shown in Table 1 areexemplary and the source of silica and/or the resulting crucible canhave lower or higher amounts of the listed impurities without departingfrom the scope of the present disclosure.

The source of quartz may be melted by any method available to those ofskill in the art and, in some embodiments, electric heaters or plasmatorches may be used to melt the source of silica and/or to maintain thesilica in a molten state. Generally the source of quartz is heated to atemperature above its softening point (i.e., the point at which quartzdeforms under its own weight and has a viscosity of about 107.6 poise)which may range from about 1500° C. to about 1700° C. and is about 1683°C. for high purity quartz (e.g., GE Type 214). Most sources of silica(e.g., sources that contain mostly silica such as about 50 wt % to about100 wt % or 95 wt % to about 100 wt % silica) are sufficiently moldableand/or flowable at a temperature of 1700° C. or more. In someembodiments, silica is heated to higher temperatures to promote flowsuch as at least about 1800° C., at least about 1900° C., at least about2000° C. or more. Silica may be melted while being exposed to argon,nitrogen or air.

Suitable vessels which may be used to hold the silica during or aftermelting may be made of any material that can withstand high temperaturesand which does not cause undesirable impurities to enter the silicamelt. Exemplary vessels may be composed of graphite or graphite coatedwith SiC or that are made of molybdenum or tungsten including molybdenumor tungsten alloys.

Once melted, the molten silica composition may be molded into the shapeof a crucible. To mold the composition, the composition typically isdischarged from the vessel in which it is held onto a mold or a mandrelused to shape the composition into a crucible. In some embodiments, amolten bead of silica may be expelled from the vessel (which may becone-shaped to promote discharge of molten silica) and the bead ispoured into a mold or onto a mandrel.

In some embodiments, the molten composition is poured into a mold.Generally the mold has a void formed therein that has a shape anddimensions that correspond to the shape and dimensions of the desiredcrucible. Alternatively, the composition may be poured onto a mandreland formed into a crucible. Typically the mandrel has a shape thatcorresponds to the inner cavity of the crucible and is arranged suchthat the portion of the mandrel that corresponds to the base of thecrucible is positioned upward. The molten silica composition may bepoured onto this portion of the mandrel to form the base of the crucibleand allowed to pour down the side of the mandrel to form the sidewallsof the crucible. In some embodiments, force is applied to the moltencomposition to force it to conform it to the shape of the mandrel (e.g.,by pushing or pressing a paddle against the composition while thecomposition is still at a moldable temperature).

By heating the composition above its softening point and allowing thecrucible to be molded while in a plastic state, the silica melt isoutgassed thereby reducing the amount of bubbles that may form duringsolidification of the crucible which results in formation of aclear-wall crucible. This is in contrast to vitreous fused silicacrucibles which are quickly heated and cooled which results in bubblesbeing frozen into the crucible causing the crucible to be opaque.

After the crucible is formed, the crucible may be maintained above atemperature of about 1285° C. to anneal the crucible and to allowstresses in the crucible to be reduced which decreases the likelihood ofcracking during cooling or future use. In other embodiments, thecrucible is annealed at a temperature of at least about 1400° C., atleast about 1500° C., at least about 1600° C. or from about 1285° C. toabout 1683° C., from about 1285° C. to about 1600° C. or from about1400° C. to about 1600° C. The temperature of the anneal should be lessthan the temperature at which the material begins to deform to preventthe crucible from losing its shape. In this regard, this temperature mayvary depending on the purity of the source of silica with higher puritymaterials deforming at higher temperatures and vice versa. The annealmay be performed for about 60 minutes or longer (e.g., about 1 to about4 hours) to allow for stresses to be relieved in the crucible.

The anneal may be performed after the crucible is formed and hasundergone partial cooling (e.g., cooling to the anneal temperature) tosolidify the crucible. Alternatively, the crucible may be cooled tobelow the anneal temperature and then heated back up to the annealtemperature.

In some embodiments, a vacuum is applied during melting, molding or theanneal processes to promote outgassing and reduction of bubbles in thecrucible. It should be noted that outgassing also occurs at ambientpressures and in some embodiments of the present disclosure a vacuum isnot applied during the melting, molding or anneal of the crucible.

After the molten composition is shaped into a crucible and after theoptional anneal, the shaped composition is cooled to room temperature.In some embodiments, the shaped composition is cooled relatively slowlyto allow stresses in the cooling crucible to be gradually relieved,which lessens the likelihood of the crucible cracking during cooling orduring future use. In some embodiments of the present disclosure, attemperatures above the strain point of the silica material (i.e., thepoint at which the material relieves internal stress in about 4 hours orhas a viscosity of about 1014.5 poise) the crucible is cooled (e.g.,from the molding temperature or the anneal temperature) such that theinstantaneous cooling rates during cooling are less than about 1°C./min. In other embodiments the instantaneous cooling rates above thestrain point is less than about 0.5° C./min, less than about 0.1°C./min, from about 0.05° C./min to about 1° C./min or from about 0.1°C./min to about 1° C./min. In this regard, the strain point of silicamay occur between about 1000° C. to about 1200° C. and is about 1120° C.for high purity silica (e.g., GE Type 214 quartz).

In this regard, the particular dimensions of the crucible may be chosenby those of skill in the art based on the particular use of the crucible(e.g., ingot diameter, crystal puller dimensions and the like).Generally most crucibles are cylindrical and have a base (which may beflat or curved) and a sidewall. Other arrangements may be used such assquare or rectangular crucibles which have more than one sidewallwithout limitation. In embodiments wherein the crucible is used to holdmolten silicon for growth of single crystal silicon ingots, thethickness of the crucible base and sidewalls may be at least about 6 mmor, as in other embodiments, at least about 8 mm, at least about 10 mmor even at least about 14 mm (e.g., from about 6 mm to about 40 mm, fromabout 6 mm to about 30 mm, from about 6 mm to about 20 mm or from about10 mm to about 40 mm).

In some embodiments, rather than forming a crucible directly from themolten composition, the molten silica composition is molded to form aplate or tube under any of the same conditions described above forforming a crucible (e.g., outgassing, annealing and/or relatively lowcooling rate). In embodiments wherein a plate is formed, the plate maybe placed above a mandrel as previously described and shaped to form acrucible, optionally while heating the plate up to or above thesoftening point of silica. In embodiments wherein a tube is used, one ofthe two end portions of the tube is shaped to form the base of thecrucible (e.g., by use of a chuck), typically while heating the endportion of the crucible which is shaped. The dimensions of the plate ortube should be chosen based on the desired dimensions of the crucible.In this regard, the plate or tube wall generally has a thickness thatcorresponds to the desired wall thickness of the crucible.

Generally, the crucible that forms after cooling is a clear-wallcrucible rather than an opaque crucible as with crucibles formed fromvitreous fused silica. The transparency results from a reduced amount ofbubbles in the crucible as described further below.

In this regard, the crucible, plate or tube that is formed from themolten composition (and the crucibles that result after shaping of theplate or tube) have a relatively low concentration of bubbles and/orhave a reduced size of bubbles. In several embodiments of the presentdisclosure, the crucible, plate or tube has less than about 70 bubbleswith a diameter greater than about 14 μm per cm³ or less than about 50,less than about 30, less than about 10 or even no bubbles with adiameter greater than about 14 μm per cm³. In some embodiments, thecrucible is substantially free of gas bubbles of a size greater thanabout 14 μm. For purposes of the present disclosure, the crucible is“substantially free” of gas bubbles when the crucible contains less thanabout 1 bubble with a diameter greater than about 14 μm per cm³. In someembodiments, at least about 75% of the bubbles in the crucible have anominal diameter of less than about 14 μm or at least about 85%, atleast about 95% or at least about 99% of the bubbles in the cruciblehave a nominal diameter of less than about 14 μm.

In this regard, it should be understood that the number of bubbles maybe determined by observing a portion of the crucible, e.g., by use of anoptical microscope, and that the amount of bubbles described hereinrefers to such a method of observation unless stated otherwise. Further,in some embodiments, two or more portions of the crucible may beobserved to determine if the threshold amount of bubbles is achieved.For instance, the number of bubbles per cm³ may be determined forseveral coupons or optical views and the concentration of bubblesaveraged over the number of views. The portions of the crucible that areobserved may be obtained by breaking the crucible into portions (i.e.,“coupons”).

In some embodiments, rather than using a molten composition to form thecrucible, a gas containing silicon and oxygen is contacted with acrucible-shaped substrate. Upon contacting the substrate, silicadeposits on the substrate and continuously grows to form a surface layerof silica on the substrate. The silicon gas may be formed by oxidizing asilicon-containing liquid or gas (e.g., silane or a halosilane such asSiF₄ or SiCl₄ or tetraethoxysilane) such as by use of a hydrogen-oxygenflame. In some embodiments, a silicon dust may form from the gaseousphase and the silicon may be oxidized and sintered to form theclear-wall crucible.

While not limited to a particular thickness, in some embodiments thesurface layer of silica that is produced has a thickness of at leastabout 1 mm or, as in other embodiments, at least about 2 mm, at leastabout 4 mm, from about 1 mm to about 7 mm, from about 1 mm to about 4 mmor from about 2 mm to about 5 mm. In this regard, silica may be formedon only a portion of the crucible (i.e., on the inner surface of thecrucible that contacts the molten material during use) and the otherportions of the crucible can be masked or otherwise made from contactingthe gas stream.

The substrate upon which the layer of silica is deposited may be made ofany suitable material for high temperature operations such as, forexample, graphite or graphite coated with SiC or fused vitreous silica(i.e., silica that is prepared by conventional methods such as bymelting sand in a mold while under relatively high vacuum). In someembodiments the substrate comprises at least about 10 wt % silica or atleast about 25 wt %, at least about 50 wt %, at least about 75 wt %, atleast about 85 wt %, at least about 95 wt %, at least about 99 wt %silica, from about 10 wt % to about 100 wt %, from about 50 wt % toabout 100 wt %, from about 85 wt % to about 100 wt % or from about 95 wt% to about 100 wt % silica.

The silica surface layer may include at least about 95 wt % silica, atleast about 99 wt % silica or even consists essentially of silica. Thesilica surface layer may contain less than about 70 bubbles per cm³ ormay contain less than about 50, less than about 30, less than about 10or even no bubbles with a diameter greater than about 14 μm per cm³. Insome embodiments at least about 75% of the bubbles in the silica surfacelayer have a nominal diameter of less than about 14 μm or at least about85%, at least about 95% or at least about 99% of the bubbles in thecrucible have a nominal diameter of less than about 14 μm.

An exemplary crucible 10 prepared in accordance with the presentdisclosure (whether by a molding or a gas deposition process) is shownin FIG. 1. The crucible 10 has an outer surface 12 and an inner surface14 for contacting the molten material. The crucible 10 has an averagewall thickness T. A surface layer extends from the inner surface 14 to adepth D1. The surface layer contains less than about 70 bubbles per cm³or less than about 50, less than about 30 or even less than about 10bubbles per cm³ or even is substantially free of bubbles with a diametergreater than about 14 μm per cm³ as explained above. In someembodiments, at least about 75% of the bubbles in the surface layer havea nominal diameter of less than about 14 μm or at least about 85%, atleast about 95% or at least about 99% of the bubbles in the cruciblehave a nominal diameter of less than about 14 μm. In embodiments whereinthe crucible is prepared by melting a source of silicon and molding themolten composition to produce the crucible, the surface layer extendsfrom the inner surface 14 to the outer surface 12. In embodimentswherein a silica layer is produced by chemical vapor deposition, D1 maybe at least about 1 mm or, as in other embodiments, at least about 2 mm,at least about 4 mm, from about 1 mm to about 7 mm, from about 1 mm toabout 4 mm or from about 2 mm to about 5 mm. The silica surface layermay contain at least about 10 wt % silica or at least about 25 wt %silica, at least about 50 wt %, at least about 75 wt %, at least about85 wt %, at least about 95 wt %, at least about 99 wt % silica, fromabout 10 wt % to about 100 wt %, from about 50 wt % to about 100 wt %,from about 85 wt % to about 100 wt % or from about 95 wt % to about 100wt % silica. The remainder of the crucible may contain the same amountof silica (such as when pouring/molding is used and there is not adistinctly different surface layer) or may be made of other materialssuch as graphite or SiC.

By using a crucible with a reduced amount of bubbles, less gas pocketsare incorporated into the ingot during crystal growth and into theresulting wafers. It should be noted that while the crucible of thepresent disclosure may be used to produce single crystal silicon ingotsby the so-called Czochralski method in which a seed crystal is contactedwith molten silicon and withdrawn to pull a silicon ingot, the cruciblemay be used for other purposes such as direct solidification (DS)processes or for production of materials other than silicon ingots.

Single crystal silicon wafers sliced from single crystal ingots preparedby use of a crucible of the present disclosure are less likely to havegas pockets which results in a reduced rejection rate of the wafers. Incertain embodiments, in a population of wafers sliced from ingotsproduced by use of the crucible, less than about 6% (e.g., less thanabout 5% or from about 4% to about 6%) have a gas pocket with a diameterof about 100 μm or less in the front surface of the wafer. Alternativelyor in addition, less than about 5.5% (e.g., less than about 5%, lessthan about 4.5%, from about 3.5% to about 5.5% or from about 3.5% toabout 5%) of wafers in the population have a gas pocket with a diameterof about 50 μm or less in the front surface of the wafer. Alternativelyor in addition, less than about 1.5% (e.g., less than about 1.3%, fromabout 0.75% to about 1.5%, from about 1% to about 1.5% or from about 1%to about 1.3%) of wafers in the population have a gas pocket with adiameter of about 30 μm or less in the front surface of the layer. Thepopulation of wafers may include at least about 25 wafers, at leastabout 50 wafers, at least about 100 wafers, at least about 500 wafers oreven about 1000 wafers or more. The likelihood of gas pockets in suchwafers relative to wafers produced by use of conventional crucibles isdescribed in Example 2 below. The wafers of the population may be in apre-processed state such as before polishing, lapping or other flatnessor surface roughness processing. For example, each wafer in thepopulation may have saw marks and/or a surface roughness of at leastabout 2 Å as measured with scan sizes of about 1 nm×about 1 nm to about100 nm×about 100 nm.

Gas pockets in the wafers may be determined by use of an IR camera andSP1 or SP2 inspection tools. In this regard, it should be noted that thesize of gas pockets in the distribution profiles described above may begreater than about 30 μm (e.g., about 100 μm to about 30 μm, from about50 μm to about 30 μm or at about 30 μm) as 30 μm is near the currentdetection limit of air pockets for SP1 and SP2 inspection tools.

The silicon ingot from which the wafers are sliced typically has aconcentration of gas pockets less than the amount of gas pockets iningots produced from vitreous silica crucibles. As the amount of gaspockets can vary radially and/or axially in the ingot, the ingot may becharacterized by the amount of gas pockets formed in wafers subsequentlysliced from the ingot. For instance, when the constant diameter portionof the ingot is sliced into wafers by a wire saw, less than about 6%(e.g., less than about 5% or from about 4% to about 6%) of the slicedwafers have a gas pocket with a diameter of about 100 μm or less.Alternatively or in addition, the ingot may have a concentration of gaspockets such that, upon subsequently slicing the constant diameterportion into wafers, less than about 5.5% (e.g., less than about 5%,less than about 4.5%, from about 3.5% to about 5.5% or from about 3.5%to about 5%) of the sliced wafers have a gas pocket with a diameter ofabout 50 μm or less. Alternatively or in addition, the ingot has aconcentration of gas pockets such that, upon subsequently slicing theconstant diameter portion into wafers, less than about 1.5% (e.g., lessthan about 1.3%, from about 0.75% to about 1.5%, from about 1% to about1.5% or from about 1% to about 1.3%) of the sliced wafers have a gaspocket with a diameter of about 30 μm or less.

EXAMPLES

The processes of the present disclosure are further illustrated by thefollowing Examples. These Examples should not be viewed in a limitingsense.

Example 1 Production of a Crucible by Tube Forming

GE 214 clear wall quartz tubing was used to form a clear-wall cruciblewith a reduced amount of bubbles. The tubing was cut to length and oneend of the tubing was molded to form the base of the crucible by heatingand use of a chuck. The tubing and resulting crucible had a diameter ofabout 32 inches (81 cm). The crucible was suitable for use in growing asingle crystal silicon ingot.

Example 2 Modeling the Likelihood that Gas Pockets are Produced inWafers Sliced from Ingots by Use of a Crucible Substantially Free ofBubbles

Modeling was performed to determine the likelihood that gas pocketswould form in wafers produced in conventional vitreous fused quartzcrucibles and in clear-wall crucibles that are substantially free ofbubbles (i.e., less than about 1 bubble of a size of 14 μm or more percm³). The prevalence of gas pockets that form in the resulting wafers asdetermined by modeling is shown in Table 2 below.

TABLE 2 Likelihood of Gas Pocket Formation in Wafers Sliced from IngotsGrown from Vitreous Fused Quartz and Clear-Wall Fused Quartz CruciblesVitreous Fused Quartz Clear-Wall Fused Crucible Quartz CrucibleIncidence of gas pockets 1.65% of wafers 1.21% of wafers with diameterless than about 30 um Incidence of gas pockets 5.80% of wafers 3.91% ofwafers with diameter less than about 50 um Incidence of gas pockets6.42% of wafers 4.25% of wafers with diameter less than about 100 um

When introducing elements of the present disclosure or the embodiment(s)thereof, the articles “a”, “an”, “the” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising,”“including,” “containing” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements. The use of terms indicating a particular orientation (e.g.,“top”, “bottom”, “side”, etc.) is for convenience of description anddoes not require any particular orientation of the item described.

As various changes could be made in the above constructions and methodswithout departing from the scope of the disclosure, it is intended thatall matter contained in the above description and shown in theaccompanying drawing[s] shall be interpreted as illustrative and not ina limiting sense.

What is claimed is:
 1. A process for producing a crucible for holdingmolten silicon, the crucible having a base and one or more sidewalls,the process comprising: forming a composition comprising molten silicaand a fining agent to prevent bubble formation, the fining agentselected from the group consisting of arsenic oxide, antimony oxide,KNO₃, NaNO₃, NaCl, a fluoride salt, a sulfate salt, and any combinationthereof in a vessel; discharging the composition comprising moltensilica and the fining agent from the vessel into a mold or onto amandrel; applying a force to the composition comprising molten silica tothereby mold the molten composition into the shape of (1) a cruciblehaving a base and one or more sidewalls, (2) a plate or (3) a tube; andcooling the molten composition to solidify the composition, wherein whenthe molten composition is molded into the shape of a plate or a tube,the plate or tube is shaped into the form of a crucible having a baseand one or more sidewalls.
 2. The process as set forth in claim 1wherein the molten composition is molded into the shape of a crucible,the composition being molded by pouring the composition into a mold. 3.The process as set forth in claim 1 wherein the molten composition ismolded into the shape of a crucible, the composition being molded bypouring the composition over a mandrel and shaping the composition intothe form of a crucible.
 4. The process as set forth in claim 1 whereinthe molten composition is annealed after the force is applied to thecomposition comprising molten silica, which molds the molten compositioninto the shape.
 5. The process as set forth in claim 1 wherein thesource of silica is melted by heating the source of silica to atemperature of at least about 1700° C.
 6. The process as set forth inclaim 1 wherein the source of silica is melted by heating the source ofsilica to at least its softening point.
 7. The process as set forth inclaim 6 wherein the softening point is about 1683° C.
 8. The process asset forth in claim 1 wherein the crucible is cooled to below the strainpoint, wherein the instantaneous cooling rates at temperatures above thestrain point are less than about 1° C./min.
 9. The process as set forthin claim 8 wherein the strain point occurs between about 1000° C. toabout 1200° C.
 10. The process as set forth in claim 1 wherein themolten composition is molded in to the shape of a plate, the methodfurther comprising heating the plate while the plate is shaped into theform of a crucible.
 11. The process as set forth in claim 1 wherein themolten composition is molded in to the shape of a tube, the tube havingan end portion that is shaped to form the base of the crucible.
 12. Theprocess as set forth in claim 1 wherein the molten composition comprisesat least about 10 wt % silica.
 13. The process as set forth in claim 1wherein the source of silica is quartz sand, quartz powder, reclaimedglass or cullet.
 14. The process as set forth in claim 1 wherein thecrucible contains less than about 70 bubbles with a diameter of at leastabout 14 μm per cm³.
 15. The process as set forth in claim 1 wherein thecrucible is substantially free of bubbles with a diameter of at leastabout 14 μm.
 16. The process as set forth in claim 1 wherein at leastabout 75% of the bubbles in the crucible have a nominal diameter of lessthan about 14 μm.
 17. The process as set forth in claim 1 wherein thecrucible has a thickness of at least about 6 mm.
 18. The process as setforth in claim 1 wherein the molten composition comprises at least about95 wt % silica.
 19. A process for producing a crucible for holdingmolten material, the crucible having a base and one or more sidewalls,the process comprising the following steps in order: discharging moltensilica from a vessel into a mold or onto a mandrel; applying a force tothe molten silica to thereby mold the molten silica into the shape of(1) a crucible having a base and one or more sidewalls, (2) a plate or(3) a tube; annealing the shaped molten silica at a temperature betweenabout 1400° C. and about 1600° C.; and cooling the molten composition tosolidify the composition, wherein when the molten composition is moldedinto the shape of a plate or a tube, the plate or tube is shaped intothe form of a crucible having a base and one or more sidewalls.
 20. Theprocess as set forth in claim 19 wherein the anneal is performed for atleast about 60 minutes.